EVOLUTION AND ITS CONSEQUENCES. 7 



large in one animal may be small in another, or vice versa ; or 

 complex in one and simple in another. The analysis of animals 

 with skeletons or vertebrata has yielded several hundred original 

 elements, out of which the 28,000 included species are con- 

 structed. Different this from the inorganic world, which can 

 only claim about sixty- two elemental substances. The study of 

 homologies is thus an extended one, and is far from complete at 

 the present day. 



2. Successional Relation. — This expresses the fact that species 

 naturally arrange themselves into series in consequence of a mathe- 

 matical order of excess and deficiency in some feature or features. 

 Thus species with three toes naturally intervene between those 

 with one and four toes. So with the number of chambers of the 

 heart, of segments of the body, tlie skeleton, etc. There are 

 greater series and lesser series, and mistakes are easily made by 

 taking the one for the other. 



3. Parallelism. — This states that while all animals in their 

 embryonic and later growth pass through a number of stages and 

 conditions, some traverse more and others traverse fewer stages ; 

 and that, as the stages are nearly the same for both, those which 

 accomplish less resemble or are parallel with the young of those 

 which accomplish more. This is the broad statement, and is 

 qualified by the details. 



4. Teleology. — This is the law of adaptation so much dwelt upon 

 by the old writers, and admired in its exhibitions by men gener- 

 ally. It includes the many cases of fitness of a structure for its 

 special use, and expresses broadly the general adaptations of an 

 animal to its home and habits. 



Of course, these laws must be all laws of evolution, if evolution 

 be true. And such they are ; but this is far from being perceived 

 by some students, for some of them were in abeyance or neglect 

 prior to the stimulus to thought caused by the appearance of the 

 ** Origin of Species." 



Forty or fifty years ago Germany had been flooded with the 

 writings of the ^^physiophilosophs." Oken and Goethe had ob- 

 tained glimpses of the wonderful " unity in variety " expressed 

 by the laws of homology. The latter saw vertebrae in the seg- 

 ments of the skull, and leaves in the floral organs of plants. He 

 had found the magic wand, and many were the harmonious visions 

 that delighted the laborious toilers among old bones and dusty 

 skins ; the patient haruspices saw omens in the intestines of birds 



